Interstitial radiation therapy has been performed since the beginning of the 20th Century. Radium was developed by Madam Curie and Alexander Graham Bell proposed the use of radium in treating tumors. Subsequently, metal needles were developed in which a radium isotope was encapsulated for insertion in close proximity or into tumors. Where the tumor was deep seated, an operation was necessary to provide access to the tumor. Such therapy had serious problems and disadvantages. The high energy of the radium isotope requird a great deal of shielding and subjected the personnel to harmful exposure. In addition, the needles tended to break as they aged resulting in the release of the radioactive contents. Since the radium isotopes had a half-life of about 1600 years, they produced an extreme contamination hazard.
Thus, efforts have been made to develop new isotopes and delivery systems making brachytherapy safer and more convenient to use. New isotopes have lower energies requiring less shielding and shorter half-lives reducing the risk of contamination.
Permanent seeds of encapsulated radon-222 having an energy level of 0.78 MEV and a half-life of 33.83 days or of encapsulated gold-198 having an energy level of 0.42 MEV and a half-life of 2.7 days have been used. More recently small seeds of iridium-192 having an energy level of 0.30 MEV and a half-life of 74.2 days and iodine-125 having an energy level of 0.028 MEV and a half-life of 60 days have been developed. Such seeds are shown, for example, in U.S. Pat. Nos. 3,351,049 and 4,323,055.
Such iridium and iodine seeds are on the order of 4.5 mm in length and 0.8 mm in diameter and are implanted in the tumor or placed in the surface of the tumor. Both of these sources have lower energies than radium that allow for simple shielding and less radiation exposure to personnel. With seeds of iodine encapsulated in a material such as titanium, shielding is provided by the surrounding tissue and the seeds can be left in the patient permanently without the need for major precautions.
Developments in delivery systems have been made in the types of applicators for placing radioactive sources either on the surface, interspread throughout the tissues (interstitial) and intercavity that is surrounded by tumor (intercavitary). Interstitial placement of seed requires the placement of hollow metal needles inserted through the normal tissues and into the tumor. Then the seeds are there after inserted into the needles, while the needles are being retracted to deposit the seeds in the tumor. Such devices are shown in the U.S. Pat. No. 4,402,308. The most commonly used instruments are the Henschke and Mick devices.
The placement of seeds on the surface of the tumors, tumors that are deep within the body require plastic catheters to be sutured over the treated area and seeds placed in the catheters by insertion of nylon tubes carrying the seeds. Catheters and seeds are removed when the proper dose is delivered. A permanent surface implant can also be preformed using I-125 seeds initially placed by hand in a woven or braided absorbable carrier such as a braided suture. The carrier with the seeds laced therein is then secured in place to form a suitable implant. This technique is time consuming and may necessitate handling of the suture as well as having the same problems as to position and retention as the catheters. In order to minimize the radiation to personnel during handling and shipping, the suture with the seeds placed therein is shielded by placing it in a curved metallic tube. See European Patent Application Publication No. 0,064,860, published 17.11.82, Bulletin 82/46.
The last method being the intercavitary placement of radioactive seeds is the method that pertains particularly to this patent. Intracavitary brachytherapy provides the ability to place radioactive material within and around a tumor to give the advantage of a high local tumor dose with normal tissue sparring as compared with an external beam apparatus alone. Intracavitary brachytherapy of gynecological tumors, due to the accessability of the vaginal and uterine cavities, allow easy insertion of radioactive sources. Today intracavitary brachytherapy has considerably improved local control and survival when using radiotherapy. It is known at this time that when cervical carcinoma is locally extensive the combination of brachytherapy and external beam has doubled survival over radical surgery alone. Today the Fletcher-Suit intracavitary applicator is the most commonly used gynecological applicator. Its development incorporates features found most important for local tumor control and minimized complications. These factors include fixation of the radioactive source geometry in relation to the normal pelvic structures, and separating the normal structures adjacent to the applicator from the sources. The system consists of a tandem used to hold radioactive sources in the uterine cavity, thus allowing a radioactive material to be located close to the tumor's center. Two hollow cylinders are placed in the vaginal fornices that hold radioactive seeds within the center of each cylinder. These cylinders are stainless steel and are actually modifications of the hollowed corks used in the Manchester system. The cylinders are attached to handles, which allow stabilization of the tandem with respect to the pelvis. It is well recognized now that the tandem and the cylinders improve the dose distribution by spacing the adjacent normal tissues from the radioactive source surface. Due to the exponential drop in dose rate as a function of distance, one is able to decrease local necrosis due to high surface doses of adjacent tissue as compared to radiation given at depth. This has been elaborated on by Rottman, M. in a publication titled "Intercavitary Applicator in Relation to Complications of Pelvic Irradiation", published in the International Journal of Radiology, Oncology, and Physics, 4:951-956, 1978.
The present invention is described to allow radiation treatment to be delivered by intracavitary means to what was previously considered to be a inaccessible site.
An example of such a site includes the brain. At the time of craniotomy a cavity is formed when the tumor is removed from the brain. The craniotomy carries a significant morbidity, and possible mortality due to anesthetic risks as well as infections and hemorrhagic complications. Thus, eliminating the necessity of a second surgical procedure to remove a radioactive source and eliminating an incision that can act as a portal for bacteria would increase the applicability of using intracavitary brachytherapy. A permanent implant would allow for immediate closure of the surgical wound and remove the necessity of a second surgical procedure.
Prior efforts to treat tumors in the brain have been by insertion of catheters and radioactive sources into the tumor or by removing the tumor by surgical techniques. In each instance, it has been difficult to insure whether proper treatment has been made and that the entire tumor has been properly treated.
Accordingly, among the objectives of the present invention are to provide a delivery system which will deliver proper radiation in instances where the tumor has been surgically removed; which system will continue to treat the surface area of the brain without necrosis of normal tissue and which can be permanently left in the brain.
In accordance with the invention, a delivery system for intracavitational brachytherapy comprises a body of material which is absorbable in animal tissue and a plurality of radioactive seeds within the body and encapsulated in the body. In one form, the body is hollow within an exterior wall defining a separate central chamber such that the hollow body exterior wall structure will accommodate growth of body tissue such as brain tissue. In another form, the body comprises a hollow body having the seeds held in the center of the body that can be inserted in the cavity to be treated. In another form, a flat sheet is attached tangentially to the hollow exterior wall to facilitate placement over the brain.